Ok so it's basically quests for specific factions and those quests gives you XP and REP and when you level that rep you unlock Faction rewards?
Short version: Yes
Long version (here we go!):
While questing/leveling, you complete quests in different zones, many of which give rep, for say, The Tillers. However, you only can ever get your rep to Friendly with the Tillers until reaching level 90. At level 90, you start getting rep for harvesting vegetables that you planted, and doing daily quests. For the Tillers, dailiy quests reward just gold, rep, and lesser charms of good fortune (converted to greaters, they give extra rolls on loot in raids, LFR, Sha of Anger, etc). One of the daily quests gives an Ironpaw token, which may be used to buy a 5-stack of a specific meat, fish, or vegetable to be used in cooking. You do daily quests to increase your rep and get rewards with that faction.
In Pandaria, there are the following factions of importance:
Order of the Cloud Serpent
The Tillers
The Anglers
Golden Lotus
Klaxxi
August Celestials
Shado Pan
The 3 factions on top give nothing of ... progression use, if you will. By that I mean, gaining rep with cloud serpent lets you learn cloud serpent riding and gives you one at exalted, with the option to purchase a couple others. Tillers exalted gives you access to some things to make your farming easier, as well as 16 plots of land (post exalted-quests). The Anglers if I remember right give some fishing-related things like a special water mount or some such.
The 4 factions at the bottom all reward gear at various stages. Golden Lotus valor point gear is all unlocked by revered, but continue to exalted and you get a "free" ilvl 489 neck from a quest available at exalted, where the gear available through revered requires valor points to purchase. Klaxxi is the same, but a "free" 489 ring at exalted. August Celestials have gear all available by revered, as well as some enchanting recipes, but at exalted there's "fun things" and a tailoring pattern for a 28 slot bag. Shado Pan gear is all available by revered again, but at exalted you get a special cloud serpent mount.
If gear is all you care about, aside from GL/Klaxxi, you really only should get your factions to revered. If you want the mounts, then you would want to continue to exalted.